Vaccines have been used for many years to protect humans and animals against a wide variety of infectious diseases. Such conventional vaccines consist of attenuated pathogens (for example, polio virus), killed pathogens (for example, Bordetella pertussis) or immunogenic components of the pathogen (for example, diphtheria toxoid). Some antigens are highly immunogenic and are capable alone of eliciting protective immune responses. Other antigens, however, fail to induce a protective immune response or induce only a weak immune response.
In the development of some vaccines and immunogenic compositions, there is a trend to use smaller and well defined immunogenic and protective materials. Recent advances in molecular genetics, protein biochemistry, peptide chemistry, and immunobiology have provided economical and efficient technologies to identify and produce large quantities of pure antigens from various pathogens. However, some such materials may not be sufficiently immunogenic, due to either their small size (especially synthetic peptides) or the lack of intrinsic immunostimulatory properties thereof.
Immunogenicity can be significantly improved if the antigens are co-administered with adjuvants. Adjuvants enhance the immunogenicity of an antigen but are not necessarily immunogenic themselves. Adjuvants may act by retaining the antigen locally near the site of administration to produce a depot effect facilitating a slow, sustained release of antigen to cells of the immune system. Adjuvants can also attract cells of the immune system to an antigen depot and stimulate such cells to elicit immune responses.
Immunostimulatory agents or adjuvants have been used for many years to improve the host immune responses to, for example, vaccines. Intrinsic adjuvants, such as lipopolysaccharides, normally are the components of the killed or attenuated bacteria used as vaccines. Extrinsic adjuvants are immunomodulators which are typically non-covalently linked to antigens and are formulated to enhance the host immune responses. Thus, adjuvants have been identified that enhance the immune response to antigens delivered parenterally. Some of these adjuvants are toxic, however, and can cause undesirable side-effects, making them unsuitable for use in humans and many animals. Indeed, only aluminum hydroxide and aluminum phosphate (collectively commonly referred to as alum) are routinely used as adjuvants in human and veterinary vaccines. The efficacy of alum in increasing antibody responses to diptheria and tetanus toxoids is well established and, more recently, a HBsAg vaccine has been adjuvanted with alum. While the usefulness of alum is well established for some applications, it has limitations. For example, alum is ineffective for influenza vaccination and inconsistently elicits a cell mediated immune response. The antibodies elicited by alum-adjuvanted antigens are mainly of the IgGl isotype in the mouse, which may not be optimal for protection by some vaccinal agents.
A wide range of extrinsic adjuvants can provoke potent immune responses to antigens. These include saponins complexed to membrane protein antigens (immune stimulating complexes), pluronic polymers with mineral oil, killed mycobacteria in mineral oil, Freund's complete adjuvant, bacterial products, such as muramyl dipeptide (MDP) and lipopolysaccharide (LPS), as well as lipid A, and liposomes.
To efficiently induce humoral immune responses (HIR) and cell-mediated immunity (CMI), immunogens are emulsified in adjuvants. Many adjuvants are toxic, inducing granulomas, acute and chronic inflammations (Freund's complete adjuvant, FCA), cytolysis (saponins and Pluronic polymers) and pyrogenicity, arthritis and anterior uveitis (LPS and MDP). Although FCA is an excellent adjuvant and widely used in research, it is not licensed for use in human or veterinary vaccines because of its toxicity.
Desirable characteristics of ideal adjuvants include:
(1) lack of toxicity; PA0 (2) ability to stimulate a long-lasting immune response; PA0 (3) simplicity of manufacture and stability in long-term storage; PA0 (4) ability to elicit both CMI and HIR to antigens administered by various routes, if required; PA0 (5) synergy with other adjuvants; PA0 (6) capability of selectively interacting with populations of antigen presenting cells (APC); PA0 (7) ability to specifically elicit appropriate T.sub.H 1 or T.sub.H 2 cell-specific immune responses; and PA0 (8) ability to selectively increase appropriate antibody isotype levels (for example, IgA) against antigens. PA0 (a) a mineral salt adjuvant; and PA0 (b) at least one other adjuvant. PA0 R1 denotes hydrogen or saturated or singly or multiply unsaturated alkyl radical having up to 50 carbon atoms; PA0 X represents --CH.sub.2 --, --O-- or --NH--; PA0 R2 denotes hydrogen or a saturated or singly or multiply unsaturated alkyl radical having up to 50 carbon atoms, PA0 R3, R4, and R5, independently of one another, denotes hydrogen, or SO.sub.4.sup.2-, or PO.sub.4.sup.2-, or other negatively charged moiety, or --CO--R6, R6 being an alkyl radical having up to 10 carbon atoms; PA0 R7 is L-alanyl, L-alpha-aminobutyryl, L-arginyl, L-asparginyl, L-aspartyl, L-cysteinyl, L-glutamyl, L-glycyl, L-histidyl, L-hydroxypropyl) L-isoleucyl, L-leucyl, L-lysyl, L-methionyl, L-ornithinyl, L-phenylalanyl, L-prolyl, L-seryl, L-threonyl, L-tyrosyl, L-tryptophanyl, and L-valyl or their D-isomers; PA0 (a) at least one antigen; PA0 (b) a mineral salt adjuvant; and PA0 (c) at least one other adjuvant. PA0 (a) means for containing a mineral salt adjuvant; PA0 (b) means for containing at least one other adjuvant; PA0 (c) means for containing at least one antigen; and PA0 (d) means for combining the mineral salt adjuvant, at least one other adjuvant and at least one antigen to produce the immunogenic composition. PA0 (a) ease of formulation; PA0 (b) effectiveness of adjuvanticity; and PA0 (c) compatibility of antigens with the adjuvant composition.
U.S. Pat. No. 4,855,283 granted to Lockhoff et al on Aug. 8, 1989 teaches glycolipid analogues including N-glycosylamides, N-glycosylureas and N-glycosylcarbamates, each of which is substituted in the sugar residue by an amino acid, as immuno-modulators or adjuvants. Thus, Lockhoff et al. (U.S. Pat. No. 4,855,283) reported that N-glycolipid analogs displaying structural similarities to the naturally-occurring glycolipids, such as glycosphingolipids and glycoglycerolipids, are capable of eliciting strong immune responses in both herpes simplex virus vaccine and pseudorabies virus vaccine. Some glycolipids have been synthesized from long chain-alkylamines and fatty acids that are linked directly with the sugars through the anomeric carbon atom, to mimic the functions of the naturally occurring lipid residues.
U.S. Pat. No. 4,258,029 granted to Moloney, assigned to the assignee hereof, teaches that octadecyl tyrosine hydrochloride (OTH) functioned as an adjuvant when complexed with tetanus toxoid and formalin inactivated type I, II and III poliomyelitis virus vaccine. Also, Nixon-George et al. (1990), J. Immunology 144:4798-4802 reported that octadecyl esters of aromatic amino acids complexed with a recombinant hepatitis B surface antigen, enhanced the host immune responses against hepatitis B virus.
Lipidation of synthetic peptides has also been used to increase their immunogenicity. Thus, Wiesmuller ((1989), Vaccine 7:29-33) describes a peptide with a sequence homologous to a foot-and-mouth disease viral protein coupled to an adjuvant tripalmityl-S-glyceryl-cysteinylserylserine, being a synthetic analogue of the N-terminal part of the lipoprotein from Gram negative bacteria. Furthermore, Deres et al. (1989, Nature 342:561) reported in vivo priming of virus-specific cytotoxic T lymphocytes with synthetic lipopeptide vaccine which comprised of modified synthetic peptides derived from influenza virus nucleoprotein by linkage to a lipopeptide, N-palmityl-S-[2,3-bis(palmitylxy)-(2RS)-propyl-[R]-cysteine (TPC).
The adjuvants and immunostimulating compounds described above may not provide for adjuvanticity for all antigens delivered to a variety of hosts under many conditions.
It would be desirable to provide adjuvant compositions that do not suffer from the disadvantages and limitations of currently available adjuvants.